Preparation And Characterization Of Modified-Graphene Oxide Based Epoxy And Polyetherimide Composites

Epoxy resin is a kind of thermosetting polymers with excellent chemical and corrosion resistance, outstanding adhesion properties, good dimensional stability and low price. It’s used in many industrial fields, such as aerospace, automotive, electron devices etc. However, usually epoxy is brittle and its low impact resistance greatly limits its application. Polyetherimide, a kind of thermoplastic polymers, has excellent properties, such as flexibility, high glass transition temperature, superior mechanical properties etc. Introduction of thermalplastic polymers(eg. Polyetherimide) into the epoxy resin is a good toughing method to overcome this weakness. The cure reaction will induce the phase separation of the epoxy/thermalplastic (EP/TP) polymer binary system. Adding inorganic fillers into the EP/TP binary system can not only control the proceeding of phase separation, but also can significantly enhance the properties of the resulting composites Graphene is a two-dimensional single layer of sp2-bonded carbons. It is widely concerned in recent years because of its superior properties such as the large theoretical specific surface area, extraordinary mechanical property, exceptional electronic, thermal conductivity etc. What’s more, graphene is a kind of low cost carbon nanofiller for it can be easily produced in large quantities from graphite, a precursor which widely exists in nature. In consideration of its excellent properties mentioned above, graphene-based nanofiller has the potential application in the preparation of high-performance polymer composites.In our thesis, modified graphene oxide was added into EP/TP binary system to study its effect on the phase separation behavior and its reinforcement of the resulting composites. Moreover, modified graphene oxide/polyetherimide composite films and modified graphene oxide/epoxy composites were prepared and their properties were characterized in detail.The thesis is divided into five parts.Chapter 1 is the introduction of the whole thesis, where we briefly introduce the properties of the main materials, some basic concepts and related researches involves in the paper. It contains four parts:(1) The introduction of graphene, including its discovery, chemical structure, properties, application etc. (2) The toughness of epoxy resin. Many different toughing methods were exhibited in this part and we mainly focus on the mechanism of the cure reaction induced phase separation (CRIPS) behavior of EP/TP binary system. (3) In this part we particularly described the recent research status of the preparation and characterization of inorganic filler modified polyimide composites. (4) The modification of epoxy resin. The recent research status of the inorganic filler modified epoxy composites was also described in detail in this part.In Chapter 2, we chose polyetherimide (PEI) as the thermalplastic polymer to tough epoxy resin, DGEBA. The concentration of PEI and the curing method for each sample were the same while different content of modified graphene oxide was added into DGEBA/PEI binary system to explore its regulating effect on the CRIPS behavior and its reinforcement on the properties of the resulted composites. Firstly the FTIR, XRD and TGA results help to confirm the successful synthesis of methylenedianiline-modified graphene oxide (GO-MDA). Then different contents of GO-MDA were incorporated into the DGEBA/PEI binary system to regulate the CRIPS behavior. According to the rheological, DSC and SEM measurements we found that the CRIPS of DGEBA/PEI systems with or without GO-MDA all followed spinodal decomposition (SD) mechanism. The introduction of GO-MDA can significantly suppress the development of phase separation and helped freeze the final morphologies of composites at an earlier stage of co-continuous structure. And the suppression effect is optimum when 3.0wt% GO-MDA was added. What’s more although the TGA results showed a slightly decrease in the thermal stability of composites, the toughness and modulus of composites were simultaneously improved with the increasing of GO-MDA according to DMA measurement and tensile test.In Chapter 3, in order to explore the effect of chemically modified graphene on the properties of PI composite films in isolation, graphene oxide-graft-polyetherimide oligomer (GO-g-PEI Oligomer) was incorporated into the commercial polyetherimide (PEI) matrix by a solvent-mixing method to prepare PEI composite films with different GO-g-PEI Oligomer concentration via a solution casting method. We proved the successful synthesis of GO-g-PEI Oligomer with the help of FTIR, XRD and TGA measurements. Digit pictures and SEM measurement were handled to explore the dispersion of filler across the composite films. Thermal and mechanical properties of the PEI composite films were characterized and it was found that as the content of GO-g-PEI Oligomer increasing from 0.25wt% to 1.0wt%, the improvement of composite films’electrical conductivity, water diffusion coefficient and water contact angle is not significant while there’s a dramatic enhancement in modulus and thermal stability for PEI composite films.In Chapter 4, GO-g-PEI Oligomer was continuously used as the nanofiller and introduced into DGEBA to prepare composites with different content of GO-g-PEI Oligomer, and methylenedianiline (MDA) was used as the curing agent. We tried to study the effect of GO-g-PEI Oligomer on the curing mechanism of DGEBA and many properties of the resulted composites were measured. The OM and SEM images of DGEBA/GO-g-PEI Oligomer composites show that modifying GO with PEI Oligomer effectively increase GO’s compatibility with DGEBA matrix, and the fracture surfaces of composites become rougher than the pure DGEBA which is beneficial to the increase of the composites’mechanical properties. This is further confirmed by the results of DMA, TMA and TGA, which present that with the addition of GO-g-PEI Oligomer, not only the modulus and glass transition temperature of composites increase but also the dimensional stability and thermal stability are improved.Chapter 5 is the summary of the thesis. Our thesis mainly concerns about the preparation and characterization of modified graphene oxide/epoxy and modified graphene oxide/polyetherimide composites. After chemical modification, GO’s compatibility in DGEBA and poly etherimide is improved. Then different kinds of modified GO is respectively introduced into DGEBA/PEI binary system, pure PEI and pristine DGEBA and we observed that the resulted composites all show significant enhancement in some properties, especially the mechanical and thermal properties. All the work in our thesis helps to indicate that using graphene-based nanofiller to modify epoxy and poly etherimide is a meaningful and promising research job.